This invention relates to the use of chemical tags to convey embedded information.
It can be very useful to be able to determine the source of articles in commerce. For example, governmental entities would often like to be able to determine whether currency is counterfeit, and to produce currency which is difficult to counterfeit. Law enforcement organizations would like to be able to undetectably mark currency used in a ransom, for example, to be able to trace the currency back to a person who placed the marked currency in commerce. Investigators, for example, would like to be able to determine from bomb residue where the materials used entered commerce, so as to be able to determine the purchaser of the components used in the bomb.
Business entities have a need to determine whether goods which are identified with them are authentic. In order to accomplish this, such entities have a need to mark their goods in a manner which is difficult to detect, and difficult to surreptitiously replicate. A solution is especially needed for easily replicated goods, such as those in printed or digital form.
Both business and government have a need to mark materials which they have placed in commerce in a machine readable form to provide a basis for taking future action. For example, currency and many consumer products have a limited life. Machine readable date information would provide a mechanism for removing such goods from commerce at a desirable time in a cost effective manner. Business also have a need from time to time to remove defective goods from commerce. A technique for uniquely labeling goods in a machine readable form would facilitate such removal.
In various aspects, the invention is intended to address these needs.
In one embodiment of the invention, there is provided a process for marking an article in a manner which is optically invisible and difficult to detect. The process is carried out by selecting a laser luminophore which fluoresces in a predetermined portion of the spectrum when exposed to an excitation light of predetermined wavelength and applying the laser luminophore to the article in an amount which is optically invisible when the article is exposed to electromagnetic radiation but which is sufficient for machine detection when the article is exposed to the excitation light of predetermined wavelength.
In another embodiment of the invention, there is provided a process for placing a chemical xe2x80x9csignaturexe2x80x9d on an article. The process is carried out by selecting a plurality of laser luminophores which fluoresce at different wavelengths in a predetermined portion of the spectrum when exposed to an excitation light of predetermined wavelength and applying the plurality of laser luminophores to a representative article in an amount which is optically invisible when the representative article is exposed to electromagnetic radiation but which is sufficient for machine detection when the representative article is exposed to the excitation light of predetermined wavelength.
The combination of laser luminophores is easily selected to yield a unique fluorescence spectral signature. The location of the peaks can be varied by taggant selection. It also varies depending on the wavelength of the excitation light, and, to some extent, on the carrier media The intensity of the peaks can be varied by taggant concentration. The identity of the taggants can be confirmed by evaluating the spectral signature at different times t after termination of the laser excitation, as well as by chromatograph/mass spec technique. Because the spectral signature obtained will change as the fluorescence decays, the primary spectral analysis should therefore be performed at a predetermined time t after laser excitation is terminated. Unless a counterfeiter has knowledge of the exact laser luminophores utilized, the wavelength of the excitation light employed in the analysis, and the time t at which is primary analysis is performed, replication of the signature would be extremely difficult. If the counterfeiter had knowledge of the time t at which the analysis was to be performed, an attempt could be made to match the signature with other chemicals by varying concentrations. This is easily countered, however, by performing a secondary spectral analysis at a different time txe2x80x2 and comparing to a standard to confirm whether the same laser luminophores were utilized, or alternatively, performing a GC/mass spec analysis. If desired, laser luminophores having rapid decay can also be employed to mask the detection of laser luminophores having slow decay.
In another embodiment of the invention there is provided a method for recording information in machine readable form. The method is carried out by selecting a desired region of the electromagnetic spectrum and dividing it into a plurality of subregions. An information class is assigned to each of the plurality of subregions. Each information class comprises a plurality of information items. A sufficient number of discrete laser luminophores which luminescence in each of the subregions are selected to encrypt the plurality of information items contained within each information class. An encryption code is assigned to each of the information items. The code is selected from nil, one selected laser luminophore, and more than one laser luminophore. An information item is selected from each of at least a portion of the information classes. A multiplicity of laser luminophores which correspond to the selected information items according to the assigned encryption code are then selected and placed in a location from they can be subsequently accessed for exposure to luminescence inducing radiation.
The encryption easily carried out by associating a predetermined information meaning with peak locations in the luminescence spectrum. For convenience, the spectrum can be separated into regions and predetermined information meanings assigned to peaks appearing in the regions. For example, a great many laser luminophores display fluorescence in the region of 300-1000 nm. This spectral region can be divided into portions and each portion used to carry a different information item. Ten laser luminophores which display distinguishable fluorescence peaks in the range of 300-450 nm can be used to designate different years. Twelve laser luminophores which display distinguishable fluorescence peaks in the range 800-1000 nm can be used to designate different months. Thirty laser luminophores which display distinguishable fluorescence peaks in the range 450-550 nm can be used to designate different companies. Thirty laser luminophores which display distinguishable fluorescence peaks in the range of 550-650 nm can be used to designate thirty manufacturing or distribution plants. Thirty one laser luminophores which display distinguishable fluorescence peaks in the range of 650-800 nm can be used to designate days in months. Peaks may be distinguishable by lambda(max), by intensity, by shape, and/or by decay characteristics.
Combinations of laser luminophores which display fluorescence in the desired region may also be used, and this greatly reduces the number of luminophores which display fluorescence in the desired region and the resolution capabilities needed to carry out this aspect of the invention. For example, a luminophore A which display fluoresce at 580 nm, a luminophore B which displays fluorescence at 580 nm, a luminophore C which displays fluorescence at 600 nm, a luminophore D which displays fluorescence at 620 nm and a luminophore E which displays fluorescence at 640 nm can be used in varying combinations and subcombinations to yield 30 spectral signatures (A, B, C, D, E, AB, AC, AD, AE, BC, BD, BE, CD, CE, DE, ABC, ABD, ABE, ACD, ACE, ADE, BCD, BDE, CDE, ABCD, ABCE, ABDE, ACDE, BCDE, ABCDE) in the region of 550-650 nm.
Bar codes typically contain 10 digits, typically integers of from 0 to 9. Four luminophores are required to encrypt 10 information units. For example, luminophores A, B, C and D, each displaying fluorescence peaks separated by about 15 nm, can be employed to encrypt the integers digits 0-9 by utilizing the subcombinations A, B, C, D, AB, AC, AD, ABC, ABD, ACD. The spectral range of 350-950 nm can be divided into 10 regions of 60 nm each and 4 such luminophores selected for each region The resulting system constitutes a chemical machine-readable xe2x80x9cbar codexe2x80x9d.
The encryption can be totally of binary form if desired. Each luminophore, by its presence or absence, would be employed to encrypt two information units, typically 0 or 1. The spectral range of 350-950 nm could be divided up into 40 portions of 15 nm width each. The number of unique encryption possibilities is 240 power by this scheme, which is on the order of a trillion possibilities. The number of possibilities can be further increased by utilizing a larger portion of the fluorescence spectrum, or by further subdividing the spectral range by improved resolution techniques, or by layering the encryption information in each portion of the spectrum based on luminophore decay rate. For example, rapidly decaying luminophores A, B, C and D can be used to encrypt any first integers 0-9 in a spectral region, and slowly decaying luminophores Axe2x80x2, Bxe2x80x2, Cxe2x80x2 and Dxe2x80x2 can be used to encrypt any second integer 0-9 (which can be same as or different from the first integer) in the same spectral region. The second information item is retrieved by detecting the fluorescence at a later time t than the first information item.
In another embodiment of the invention there is provided a composition of matter comprising a carrier medium, and a multiplicity of laser luminophores in the carrier medium. Each of the multiplicity of laser luminophores luminesces within the spectral range of 300-1000 nm and each laser luminophore is spectrally distinguishable from the other laser luminophores by its luminescence characteristics. At least one laser luminophore exhibits a spectral peak within each of the spectral ranges of 300-550 nm, 550-750 nm and 750-1000 nm.
The just described multiplicity of laser luminophores can also be used to provide a machine readable label by impregnating them on substrate sheet suitable for use as a label, according to a further embodiment of the invention.
In yet another embodiment of the invention, there is provided a composition of matter which contains a further level of encryption at the molecular level. The composition is formed by a carrier medium containing at least one laser luminophore. The laser luminophore contains at least one non-radioactive isotopic atom in an amount which is not naturally occurring.
In this embodiment of the invention, a secondary level of encryption can be carried out by utilizing tagging agents which have been isotopically enriched at one or more locations in the molecule, such as by deuterium labeling, and evaluating the mass spectrum for characteristic peaks indicative of molecular fragments carrying a non-naturally occurring distribution of isotopic atoms.
In yet another embodiment of the invention, there is provided a process for detecting a laser luminophore carried in or on a medium. The laser luminophore emits a fluorescence spectrum which has at least one characterizing peak when irradiated by an exciting light. The medium is exposed to the exciting light so as to cause said laser luminophore to emit its fluorescence spectrum. At least the characterizing peak in the fluorescence spectrum is detected. The invention is characterized in that the characterizing peak is in the spectral range of about 600 to about 2500 nm, and the exciting light has a wavelength in the range of about 200 to about 600 nm.
In another embodiment of the invention, there is provided a process for reading information encrypted into or onto a medium by a plurality of discrete laser luminophores. Each of the discrete laser luminophores is characterized by emission of a fluorescence spectrum in response to exposure to exciting light which has at least one characterizing peak which differentiates its spectrum from the spectra of the other discrete laser luminophores of the plurality. The process is carried out by exposing the medium to exciting light so as to cause the plurality of discrete laser luminophores to emit their respective fluorescence spectra. A predetermined portion of the emitted spectrum is analyzed in a first portion of a fluorescence analysis. A first information meaning is assigned to the results of the first portion of the fluorescence analysis according to a first according to a first encryption correlation. A predetermined portion of the emitted spectrum is then analyzed in a second portion of a fluorescence analysis. A second predetermined information meaning is assigned to the results of the second portion of the fluorescence analysis according to a second encryption correlation.
In still another embodiment of the invention, there is provided a process for sorting articles based on the use of laser luminophores. There is provided a stream of articles at least a portion of which carry a combination of laser luminophores which emit a fluorescence spectrum in response to exposure to exciting light. The stream of articles is exposed to exciting light, one at a time, so as to cause the combination of laser luminophores carried by any one of the articles to emit a fluorescence spectrum. For each of the articles which emit the fluorescence spectrum, a plurality of peak locations in the emitted fluorescence spectrum is determined. These peak locations are then correlated with information selected from the group consisting of binary information, alpha-numeric information, date information, and origin information. The articles are then sorted based on the correlation.